Photosensitive flasher circuit



F I P 8212 X R 3 ,3 89, 29 7 June 18, 1968 R. HAYDEN 3,389,297

PHOTOSENSITIVE FLASHER CIRCUIT Filed Oct. 1, 1965 L/ l i I I I S Re i 2 LEFT 3/R/6'HT I c 0F Ls F i i 3 L2 L4 LAMP CURRENT (LZ,L3,

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United States Patent 0 4 Claims. 6|. 315-452 ABSTRACT OF THE DISCLOSURE A fiasher circuit for a load lamp is provided by a photosensitive device which in response to light from a light source controls a relay to deenergize the light source and energize the load lamp and in response to a dark condition of the light source to permit the relay to reenergize the light source and deenergize the load lamp.

This invention relates to a flasher circuit for use, for example, in automobile turn indicators.

There are many known devices for causing signal lamps to flash, particularly in flashing turn signalling devices for automobiles where intermittent periodic current fiow through an electrical circuit is required. This has been achieved previously by provision, for example, of temperature-responsive snap switches, sometimes in conjunction with electromagnets. It is also known that delay relays and resistance-capacitance delay circuits have been used to create circuit interruptions and, therefore, provide useful circuits for flashing lamps or for any other purpose for which a circuit must be continuously interrupted. However, previously known flasher circuits must be adjusted after assembly to set the frequency and the duty cycle; at present, a significant proportion of the time required to manufacture known flashers is spent in such adjusting. In resistance-capacitance type units, temperature will in general affect both the capacity and the resistance of the resistor and as the temperature rises, frequency drops. A further disadvantage of known devices is undue consumption of electricity, up to l ampere is consumed in the operation of a hot wire flasher. It has also been found that supply voltage variations in present units affect their operation considerably.

The present invention overcomes these disadvantages by providing a flasher circuit which, in its broadest aspect comprises the parallel combination of a high resistance lamp, of a relay coil in series with a photosensitive resistor cooperating with the high resistance lamp, and of relay contacts co-operating with the relay coil. By providing current through the high-resistance lamp, the conductivity of the photoresistor, in response to the light emitted from the lamp, increases to permit sufiicient current to flow through the relay coil to close its contacts, thereby providing a current path through the contacts to the controlled device (e.g. signal lamp) and at the same time cutting off current to the high-resistance lamp. As a result, the conductivity of the photoresistor decreases, reducing current fiow to the relay coil and thus causing the contacts to open. This completes the cycle.

It will be appreciated that the circuit according to the invention requires fixed value components and consequently necessitates no adjusting after assembly. The present flasher circuit is therefore relatively economical due to this ease of manufacture. It is also relatively efficient and economical to operate because only a few milliamperes are required to operate the circuit. By using low current, the present flasher circuit affords a more stable frequency of operation than heat-operated units, whose frequency varies depending on the rapidity of dissipation of heat.

Patented June 18, 1963 ice The present invention has the additional advantage that no warm-up time is necessary; the circuit will start operating immediately.

In order that the invention may readily be carried out. one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which FIG. 1 is a schematic diagram of one embodiment of a flasher circuit according to the invention adapted for use with the electrical system of an automobile; and

FIG. 2 is a graph showing the current variation with time of the front and rear lamps of the flasher circuit of FIG. 1.

In FIGURE 1, the circuit shown comprises a battery B connected in series with the combination of three parallel branches 1, 2 and 3. Branch 1 consists of a high-resistance lamp L1. Branch 2 comprises the relay coil RC of a relay R in series with a photosensitive resistor PR of high resistance, (e.g. cadmium sulfide cell). The photoresistor PR is enclosed in with the lamp L1 in an appropriate enclosure E which prevents light other than that emitted by lamp L1 from falling on the photoresistor PR. Both branches 1 and 2 are in parallel with the third branch 3 containing the normally open contacts C of the relay R. The parallel circuit of branches 1, 2 and 3 is connected in series with a three-position switch S which may connect the flasher circuit in one ON position to signal lights L2 and L3 which may be, for example, the front and rear left-turn indicator lamps of an automobile, and in its other ON position to signal lights L4 and L5 which may be, for example, the right-turn indicator lamps.

The normal operation of the flasher circuit of FIG. 1 is as follows:

When switch S is closed, through either the leftor right-hand path to ground, e.g. where the driver of a car wishes to signal a turn, current from battery B is supplied to branches 1 and 2 of the parallel circuit. However, the initial resistance of the two branches is too high to permit enough current to flow through the signal lamps to cause them to emit perceptible light. The high-resistance lamp L1 will glow causing light to fall on the photosensitive resistor PR, thereby decreasing linearly, or otherwise, its resistance. The decreased resistance of element PR will allow sufficient current to flow through relay coil RC to close contacts C, thus permitting current to flow through the signal lamps in a low-resistance path. The current therefore causes the signal lamps to glow and thereby to give a visible signal.

With the major portion of the battery current flowing through closed relay contacts C, the light output of the high resistance lamp L1 is substantially decreased. With the reduction in this light output from lamp L1, the resistance of photosensitive resistor PR increases so that the current through relay coil RC decreases until relay contacts C open, thereby extinguishing lamps L2 and L3. The cycle is repeated until switch S is finally opened cutting off the current from battery B to the circuit.

Relay R may preferably be designed as a slow-open" relay, i.e. contacts C do not open immediately upon cessation of current through coil RC but rather after a slight time delay. This provides a relatively long glow time for the signal lamps relative to the total time for each cycle.

The current through lamps L2 and L3 (say) is roughly as shown in FIG. 2 under the preferred conditions of a slow-open relay. When switch B is closed at time t current gradually increases until at time t, relay contacts C close and the current increases substantially, causing lamps L2 and L3 to glow brightly. Relay contacts C re main closed because of the slow-open" design until time 1 at which time they open, causing a substantial decrease in the current flowing through lamps L2 and L3.

The resistances of the lamp L1 and the series combination of the coil RC and photoresistor PR, the minimum curent required through coil RC to close contacts C, and the delay characteristics of the slow-open relay contacts C may be varied to meet the frequency and glow-time requirements of the particular circuit with which the flasher circuit according to the invention is used.

Instead of a slow-open" relay, an alternate could be the proper design of a seed type lamp that would be slow coming up to brillance and slow in extinguishing itself.

While there has been illustrated and described a preferred embodiment of the invention, it should be understood that the invention is best described by the following claims.

I claim:

1. A flasher circuit comprising the parallel combination of a high-resistance lamp, a relay coil in series with a photosensitive resistor having resistance varying inversely with the intensity of light emitted from said highresistance lamp, and relay contacts operating to short circuit the parallel combination when current passing through said relay coil reaches a predeterined value.

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2. A flasher circuit comprising in series a source o direct current, the parallel combination of a high-resistance lamp, a relay coil in series with a resistor having resistance varying inversely with the intensity of light emitted from said high-resistance lamp, and relay contacts being rendered operative by said relay coil when the magnitude of the direct current passing therethrough reaches a certain predetermined value to short circuit the parallel combination; and at least one light source connected at the output of said parallel combination.

3. A flasher circuit as defined in claim 2 wherein the relay contacts close when the current passing through the relay coil reaches said predetermined value.

4. A flasher circuit as defined in claim 3 wherein the relay contacts are designed as slow-open contacts.

References Cited UNITED STATES PATENTS 2,978,588 4/1961 Mitchell et al 317l24 X 3,206,650 9/1965 Miller et al. 315159X FOREIGN PATENTS 515,764 5/1921 France.

DAVID J. GALVIN, Primary Examiner. 

